... well, I've probably
read several dozen, but asking me to remember them all is an entirely different proposition :V Still I'll mention/re-mention a few, while I'm here and vaguely conscious.
Off-the-top-of-head completed stuff:
Acceleration (Railgun/Worm) was thoroughly engaging. Brutal pacing, all sorts of shit going down, just something of a train wreck in motion.
Hope Through Overwhelming Firepower (Diebuster/worm) is another complete, fairly fun, one, in the worm sphere of things. Pretty sure both of these have been mentioned up-thread.
I actually finished
Hybrid Theory, which was
entirely too good given its premise (Massive multicrossover, Male self-insert into female canon character, buncha' other stuff -- the setup and setting is basically just a glorious mess) and faintly gargantuan length, and
These Black Eyes (though it had a sequel) -- the latter was rather episodic in nature, but had some pretty amazing "episodes". Actually having finished both is something of a thing in itself, considering the first is ~1.3 million words long, and the second
twice that, but they're both definitely complete.
Mentioned this a bit upthread -- fire emblem more-or-less character piece. Quite fuzzy, pretty damn good read.
You can cheerfully check out
nonjon as someone with several completed works to their name. Mostly does/did harry potter stuff, lots of it pretty wildly out of character, but much of it is pleasingly amusing nonetheless.
This is complete, and from what I recall it was pretty amusing -- Something Wicked This Way Comes, a Disgaea/Harry Potter crossover. Can't recall if it deserves content warnings, though -- near as I can tell, I finished reading it back in at most 2013. M rating, though, so fair warning gods know what's actually in there.
Hill of Swords has been mentioned upthread, probably several times :V
This is done -- Mass Effect/Eva crossover, pretty solid character piece.
Pretty sure it's NSFW in places, though.
A Green Sun Illuminates the Void finished, sorta'.
Probably mentioned Thousand Shinji somewhere up there, it's done and pretty fun. WH40k/Eva Xover, with shinji starting off more or less as a Thousand Sons trained psyker.
This bugger has something like a half dozen completed sizable Megaman fics, mostly set in the X timeline, iirc. It's been a long damn time since I've read them (like, literally over a decade for some), but from what I recall they were mostly pretty damn ace.
This was pretty damn good, though I can't comment on its sequel. Harry Potter/Metroid crossover, and a fairly solid romp despite the odd premise.
...
Naruto Genkyouien is finished, and the writing
is by and large pretty decent. Haven't gotten around to actually finishing reading the thing, so I can't comment on a fair amount of the latter half or so >_>
This finished, apparently. Rough in places, but the premise was pretty damn interesting and despite some same-y writing from the author, it was one of those I lumped in as "surprisingly good", so... sure.
and now the headache as drained my will to continue ransacking 17 years of fanfiction memories for completed stuff that was decent enough, so i'm done now, do enjoy. though that said, there's definitely a
lot more -- i'm quite sure there's at
least six or seven solid complete ranma ones i didn't mention, just as an example. complete fics are definitely less common, but "less common" when it comes to the massive weight of fanfiction still means "at least hundreds", and that's just sticking to the larger ones.
also fanfiction.net has filters, and one of those filters is for "complete"
and for non-complete stuff this made me remember and I don't think has been mentioned, have
an example.